Real estate trends

The Washington Post regularly tracks housing sales and prices throughout the Washington area each Saturday in the Real Estate section, comparing information collected for each residential Zip code from each time period last year with that for the corresponding time period in 2010.

The chart and map this week compare single-family house and townhouse sales figures in Prince William County from January through March 2009 with those for the corresponding period in 2009, showing the total number of sales, the median prices and the changes in the medians. The median is the point at which half of the sales prices were higher and half lower. Condominiums were excluded.

The sales and price information, collected by The Washington Post, is based on sales recorded in local government offices. That information is in the chart on the right. It excludes some types of transactions, particularly those that are not at market price.

As with any statistical compilation, the greater the number of transactions, the more reliable the statistical trend. Moreover, at any given time there may be more sales activity in certain market niches or price ranges, for instance starter homes or high-priced houses, than at other times, and this may influence a median price from year to year.

The map provides a snapshot of price trends throughout the geographical area covered by each week's information.

ON THE WEB

For up-to-date home sales and tax assessments, real estate news and community profiles, visit www.washingtonpost.com/realestate.